DNS Failures Kill Everything — Monitor Yours Automatically

C:\Scripts\DNSHealthMonitor.ps1

# DNS Health Monitor
# Automate & Operate — automateandoperate.com

# Settings — update these
$from = "[email protected]"
$to = "[email protected]"
$smtpServer = "your.smtp.server"
$smtpPort = 587
$username = "[email protected]"
$password = ConvertTo-SecureString "yourpassword" -AsPlainText -Force
$credential = New-Object System.Management.Automation.PSCredential($username, $password)
$logFile = "C:\Logs\DNSHealthMonitor.log"

# DNS servers to monitor
$dnsServers = @(
    "192.168.1.1",
    "192.168.1.2",
    "8.8.8.8"
)

# Test records to resolve — use known reliable hostnames
$testRecords = @(
    "google.com",
    "microsoft.com",
    "yourinternaldomain.local"
)

# Response time threshold in milliseconds
$responseTimeThreshold = 500

# Create log folder if missing
if (-not (Test-Path "C:\Logs")) {
    New-Item -ItemType Directory -Path "C:\Logs"
}

$timestamp = Get-Date -Format "yyyy-MM-dd HH:mm:ss"
$report = @()
$failedServers = @()

foreach ($dnsServer in $dnsServers) {
    foreach ($record in $testRecords) {
        try {
            $startTime = Get-Date
            $result = Resolve-DnsName -Name $record -Server $dnsServer -ErrorAction Stop
            $responseTime = [math]::Round(((Get-Date) - $startTime).TotalMilliseconds, 0)

            $status = if ($responseTime -gt $responseTimeThreshold) {
                "SLOW"
            } else {
                "OK"
            }

            $report += [PSCustomObject]@{
                DNSServer    = $dnsServer
                TestRecord   = $record
                ResolvedIP   = ($result | Select-Object -First 1).IPAddress
                ResponseTime = "$responseTime ms"
                Status       = $status
            }

            Add-Content -Path $logFile -Value "$timestamp — $dnsServer — $record — ${responseTime}ms — $status"

        } catch {
            $report += [PSCustomObject]@{
                DNSServer    = $dnsServer
                TestRecord   = $record
                ResolvedIP   = "FAILED"
                ResponseTime = "N/A"
                Status       = "FAILED"
            }

            if ($failedServers -notcontains $dnsServer) {
                $failedServers += $dnsServer
            }

            Add-Content -Path $logFile -Value "$timestamp — $dnsServer — $record — FAILED — $_"
        }
    }
}

# Build email body
$emailBody = "DNS Health Monitor Report — $timestamp`n"
$emailBody += "Servers checked: $($dnsServers -join ', ')`n"
$emailBody += "Test records used: $($testRecords -join ', ')`n"
$emailBody += "Response time threshold: $responseTimeThreshold ms`n`n"
$emailBody += "RESULTS:`n"
$emailBody += "=" * 60 + "`n`n"

foreach ($entry in $report) {
    $emailBody += "DNS Server:    $($entry.DNSServer)`n"
    $emailBody += "Test Record:   $($entry.TestRecord)`n"
    $emailBody += "Resolved IP:   $($entry.ResolvedIP)`n"
    $emailBody += "Response Time: $($entry.ResponseTime)`n"
    $emailBody += "Status:        $($entry.Status)`n"
    $emailBody += "-" * 40 + "`n"
}

if ($failedServers.Count -gt 0) {
    $emailBody += "`nFAILED DNS SERVERS — ACTION REQUIRED:`n"
    $failedServers | ForEach-Object { $emailBody += "  !! $_`n" }
}

$emailBody += "`nAutomate & Operate — automateandoperate.com"

# Set subject based on results
$subject = if ($failedServers.Count -gt 0) {
    "DNS ALERT: $($failedServers.Count) DNS server(s) failing on $env:COMPUTERNAME"
} else {
    "DNS Health Report — All servers responding normally"
}

Send-MailMessage `
    -From $from -To $to `
    -Subject $subject `
    -Body $emailBody `
    -SmtpServer $smtpServer -Port $smtpPort `
    -UseSsl -Credential $credential

-ExecutionPolicy Bypass -File "C:\Scripts\DNSHealthMonitor.ps1"

powershell.exe -ExecutionPolicy Bypass -File "C:\Scripts\DNSHealthMonitor.ps1"